Something I should note: Once you do your level 10 main class quest, you can freely change classes. You'll have to visit the class guilds and talk to their receptionist to unlock the quest, but afterwards you can swap any time outside of combat or instances by changing to a weapon you have the levels to wield. Of note, every class (including crafting and gathering) have their own levels, and what armor and weapons each can wield is dictated by the class's level. So, if you're a level 20 thaumaturge, and swap to a level 1 archer, you need a level 1 bow, and level 1 equipment to wear.

Due to the ability to change classes, having multiple characters on one account is kinda discouraged. In fact, one big reason to have all classes on the same character is so that if you get a dungeon drop while playing one class, you can use it on another one (dungeon drops typically cannot be traded)